[QUEUED v20160212 14/19] stm class: Fix unlocking braino in the error path

[Alexander Shishkin]

If an illegal attempt is made to unlink stm source device from an
stm device, the stm device's link spinlock mistakenly remains locked.
While this really shouldn't happen (there's a warning in place), the
locking should remain in order so that we can still recover from this
situation if it indeed does happen.

This patch unifies the unlocking in the exit path of
__stm_source_link_drop() to fix this.

Reported-by: Laurent Fert <laurent.fert@xxxxxxxxx>
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
---
 drivers/hwtracing/stm/core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 385db65994..fb5a6a582b 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -816,10 +816,8 @@ static void __stm_source_link_drop(struct stm_source_device *src,
 	spin_lock(&stm->link_lock);
 	spin_lock(&src->link_lock);
 	link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
-	if (WARN_ON_ONCE(link != stm)) {
-		spin_unlock(&src->link_lock);
-		return;
-	}
+	if (WARN_ON_ONCE(link != stm))
+		goto unlock;
 
 	stm_output_free(link, &src->output);
 	list_del_init(&src->link_entry);
@@ -827,6 +825,7 @@ static void __stm_source_link_drop(struct stm_source_device *src,
 	stm_put_device(link);
 	rcu_assign_pointer(src->link, NULL);
 
+unlock:
 	spin_unlock(&src->link_lock);
 	spin_unlock(&stm->link_lock);
 }
-- 
2.7.0